In order to avoid bone resorption it has become standard practice to mount a major dental prosthesis, for instance a full plate, on a structure that itself is carried on implants set right in the patient's bone structure and projecting up through the gingival tissues. Thus the patient's actual mandible carries the prosthesis in a manner akin to the anchoring of the patient's one-time own teeth in his or her jaw.
Such a standard structure has several anchors that are surgically implanted in the mandible. Typically three anchor locations are employed, one at each ramus bone and one at the symphysis, that project up through the gingival tissue and are joined by bars which extend generally parallel to the occlusal plane and to which is clipped the dental prosthesis.
In European patent document 393,324 based on a German priority of 10 Apr. 1989 the anchors are constituted as posts having at their upper ends small seats in which small ball heads of connecting bars can be clamped. Such an arrangement is not very strong, the posts must be exactly positioned, and the bars are fairly complex telescoping structures that require that the posts be relatively widely spaced. Furthermore the offset mounting of the ends of two bar ends on a single post makes it difficult to conform the structure to a tightly curved arch.
In U.S. Pat. No. 3,748,739 of Thilbert four implanted anchors are joined by complicated articulated bars. More than four anchor locations is impossible due to the complexity of the coupling bars so that resorption of bone between the anchors is a problem.
Another system is described in U.S. Pat. No. 4,062,119 of Linkow. It uses three anchor points that are joined by a massive structure. Substantial surgery is needed to seat each of the anchors, but the intermediate bone is subject to resorption. Furthermore the three anchors must be accurately positioned for the structure to fit properly.